As automobile technology develops, various technologies for enhancing fuel economy and improving power output have appeared on the scene. For example, there are: the variable induction system (VIS), which controls the length and cross section of the induction passage according to the number of revolutions and load of the engine; the variable valve timing (VVT) system, which controls valve timing according to the number of revolutions and load of the engine; the variable valve lift (VVL) system, which controls valve deflection according to the number of revolutions and load of the engine; etc.
In general, when an engine rotates at a high speed, a large intake of air is desirable. However, when it rotates at a low speed or a constant speed, a large intake of air reduces the flow speed, causing the vortex in the combustion chamber not to occur smoothly, thus reducing the inhalation efficiency.
The variable valve lift system, which was developed in order to solve the afore-mentioned problem, increases inhalation by driving the valve at high lift when the engine turns at a high speed, and decreases inhalation by driving the valve at low lift when the engine turns at a low or constant speed while increasing flow speed, thus realizing high fuel economy, high power output, and high efficiency.
Here, valve lift is an important factor in determining the amount of air inhalation and the amount of exhaust gas emission, and represents the separation distance between the valve face and the valve seat. In other words, the greater the valve lift (high lift), the greater the amount of air flow into the cylinder and the greater the amount of exhaust gas emission, thus raising the intake-outtake efficiency.
The variable valve lift system generally uses hydraulic pressure in order to control valve lift. Such a hydraulic type variable valve lift system includes an oil pump, an oil control valve (OCV), an oil filter, and a valve lift control actuator.
However, with the aforementioned hydraulic type variable valve lift system, if a constant hydraulic pressure is not obtained in the hydraulic line connecting the oil control valve and the valve lift control actuator, the control of valve lift may become impossible, or unreliable even if control is possible.